The invention herein relates to refractory fiber thermal insulation compositions suitable for use in water-containing packages known as "wet packs".
Refractory fiber thermal insulation blankets are normally relatively soft and resilient with virtually no ability to be self-supporting when placed in a vertical position. For certain applications, however, it is imperative that a refractory fiber composition be self-supporting, such that the finished product (for instance, a combustion chamber lining) can stand upright without external support. To this end, the prior art has impregnated blankets of fiber with various binder compositions, including various siliceous materials. The refractory fiber blanket is molded to the desired configuration and the binder is then set by heating for forming a rigid self-supporting body.
Commonly such moldable blankets have been packaged for use in the form of "wet packs". The blanket which is impregnated with an aqueous binder system is placed in an air-tight and water-tight container, such as a plastic bag. In this form the binder remains essentially unset and the moldable product can be shipped and stored relatively readily. When the customer is ready to use the product he opens the container, molds the impregnated blanket to the desired shape, and causes the binder to become set.
Certain problems have become known with the "wet pack" type of packaging, however. Because the wet pack must remain flexible and moldable until such time as the customer intends to use it, the binder system must be of a non-gelling type. However, the particles in non-gelling binders have a decided tendency to migrate to the surface of the fiber body during drying. The resultant molded product thus has binder only in the outer surface layers and as a result is substantially weaker than similar articles made from gelled binder systems where the binder is retained throughout the fiber body. In addition, during shipping and storage wet packs of fiber are often subjected to low temperatures which can cause freezing of the aqueous portion of the binder system. Such freezing of the water causes the solid binder material to precipitate out of the system and the fiber body. This also results in a substantially weakened product by the time the customer is ready to use the fiber.
One use of refractory fiber web packs is as thermal insulation for automobile turbine engines. However, it has been found quite difficult to make prior art wet pack materials adhere satisfactorily to the metal surfaces of the engine blocks. If good adhesion is not obtained, there is a decided decrease in thermal efficiency of the insulation.